My preference is candied ginger. You can buy it in any spice aisle. I take a bunch and put it in a zip lock bag to carry with me. Ginger does settle the stomach, but it's also a blood thinner, so people need to be aware of that. If I'm going for a small boat trip (eg whale watching) I also take a Bonine tablet before the event. If it's gonna be real rough - I'll wear wrist bands too. You can never be too safe!